To work in the extremely cold temperatures of outer space, astronauts must wear protective space suits so that body heat may be maintained. However, liquid cooling of such garments is necessary in order to avoid heat build-up within the suit, which can cause discomfort or heat exhaustion, particularly during periods of physical activity.
The prior art has often used tubes within the garment to carry water which conducts excessive body heat away from the astronaut. A heat exchanger for the heated water often takes the form of a sublimator which forms specks of ice on the back of the garment. Heat transfer from the heated water of the space suit tubes causes the specks of ice to undergo a phase change --to vapor. The vaporization of the ice enables the body temperature of an astronaut within the suit to be comfortably regulated. However, a problem with the use of sublimators occurs when the evaporated ice becomes suspended in space as a vapor, due to the lack of gravity. Oftentimes, this vapor will become deposited on an astronaut's visor or optical equipment he carries, which is obviously disadvantageous.
In order to replace the sublimator design of the present invention, one might consider employing a heat storage system which avoids the emission of vapor in the immediate space of a working astronaut.
Heat can be stored effectively and efficiently in a constant temperature heat sink by pumping a working fluid through ice. As the ice melts it cools the working fluid and uses the heat to change from a solid to a liquid phase. If water were used as a working liquid and if an astronaut is relatively still and therefore not generating excess heat, there is a likelihood that water flowing through the space garment tubes will freeze at points, particularly near the ice. This would require the utilization of special heaters to ensure that the working fluid (water) does not freeze. The utilization of such heaters will then use up some of the ice storage capacity as well as adding extra complexity to the system.
A logical extension of this reasoning suggests the substitution of another liquid for water. Although certain liquids could function properly to achieve a liquid cooling effect of an astronaut's garment, such liquids, such as anti-freeze, are toxic when breathed in high concentrations for a prolonged period of time. Since such liquids would be circulating within a space suit, the chances of accidental leakage preclude their use.